The invention relates to a downhole subsurface safety valve device in an oil or gas well. The invention is particularly suitable for use in subsea wells.
In an oil or gas well a barrier has to be established down in the well in order to safeguard against an uncontrolled efflux of the hydrocarbons. In the production tubing, therefore, a valve is mounted which is open during normal operation, but which can be closed if it becomes necessary to open the well, for example for a workover.
Downhole safety valves are in the form either of ball valves or flap valves. They are normally hydraulically operated by means of a hydraulic line, which extends down into the well along the tubing in order to supply hydraulic fluid to a piston in a valve actuator for opening the valve. The valves are usually arranged in such a manner that they are automatically closed when there is a loss of operating fluid.
An example of such a valve is disclosed in U.S. Pat. No. 5,862,864.
Such valves are normally very reliable. One drawback, however, is that the supply line is highly vulnerable to damage, which may be incurred down in the well. The supply line is arranged along the outside of the tubing. A leakage in the supply line causes the valve to close without the possibility of opening it again. In this case the tubing has to be removed from the well, and this is a highly complicated and expensive operation.
Solutions exist for lowering an additional valve, but it needs to have a smaller through-flow opening than the old one. Another solution is to lay the supply line in a channel inside the wall of the tubing, but this makes the tubing expensive and it is difficult to screw the pipes together so that the channels are in alignment. In addition complex seals have to be established between the pipes.
A second drawback with the present valves is that they cannot be operated manually. Valves on the Christmas tree, e.g., are equipped with manual override, thus enabling the valve to be opened or closed by means of a remotely operated subsea vessel, a so-called ROV.
Thus it is an object of the invention to provide a valve that can be operated without the use of hydraulic fluid and from the outside of the well. This is achieved by means of the present invention by a valve actuator being placed in or on the Christmas tree with a mechanical connection down to the valve""s kelly bushing. The mechanical connection is a member extending in the well""s longitudinal direction, which can either be moved axially or rotated in order to operate the valve.
This provides a number of advantages. For example, should a fault arise in the actuator, it can easily be replaced. A second major advantage of the invention is that the actuator can be equipped with a manual override. The valve can thereby be closed by means of an ROV in the event of failure of the actuator.